Internal combustion engines are used to convert the energy contained in a fuel into volume change work. For this purpose, the internal combustion engine has at least one combustion chamber, in which the fuel is burnt. The volume expansion that occurs during combustion is then converted into a rotary motion, which can be used for propulsion of an on-road vehicle.
In order to obtain a combustible mixture for the combustion process, the fuel is mixed with ambient air, in particular with the oxygen (O2) contained therein. In direct injection (DI) engines, fuel is injected directly engine cylinders, and mixing of fuel and oxygen takes place almost exclusively within the combustion chambers.
Internal combustion engines including DI fuel systems may be divided into applied-ignition engines and self-ignition engines. In this context, spark-ignition engines are applied-ignition engines since the mixture situated in the combustion chamber is initially compressed and then ignited actively by extraneous means, for example by a spark plug. In contrast, diesel engines are referred to as self-ignition engines. In the case of these engines, compression centers on the air supply to the combustion chamber, which undergoes a rapid rise in temperature as a result. The resulting temperature level is sufficient to ignite the diesel fuel which is then to be injected into the combustion chamber filled in this way with heated air.
In DI fuel systems, engine fuel may be pumped out of a fuel tank by a lift pump. The lift pump propels fuel towards a fuel rail before being injected by fuel injectors. DI systems generally have a single manifold (common fuel rail) for each row of cylinders. In the description herein, said manifold can be designed as an elongate or ball-type rail. Common rail injection arrangements are usually used with internal combustion engines operated with diesel fuel. Nonetheless, they can also be used in an appropriate configuration for spark-ignition engines operated with gasoline fuel.
Further, DI fuel systems typically include a high-pressure pump upstream of the fuel rail to further pressurize the fuel pumped out of the fuel tank by the lift pump before the fuel reaches the fuel rail. Thus, a substantially continuous buildup of a fuel pressure may be produced by the high-pressure pump within the fuel rail. Individual injection nozzles are fluidically connected to the fuel rail to deliver pressurized fuel from the fuel rail to each combustion chamber. These nozzles may be electronically controlled to open and close at a desired rate over a required period of time to deliver a desired fuel volume. In this way, some of the fuel available under pressure at the individual injection nozzles is discharged into the respective combustion chambers as the internal combustion engine runs.
The high-pressure pump is generally connected in a torque-transmitting manner to the internal combustion engine. Thus, the operating state (e.g., speed) of the high-pressure pump, and therefore the amount of pressure added to the fuel being supplied to the fuel rail, depends directly on the operating state of the internal combustion engine. In other words, the high-pressure pump may stop operating when the internal combustion engine is switched off in a stop phase. Particularly in conjunction with stop-start systems for internal combustion engines, which are provided to lower fuel consumption, there are increased requirements on the performance of common rail injection arrangements. During the stop phase in stop-start systems when the high-pressure pump is off, the pressure in the fuel rail can fall. In some examples, the pressure in the fuel rail can drop below a minimum pressure required for injection during the stop phase. To start the internal combustion engine, it is therefore necessary to build up again and/or maintain the required fuel pressure within the common rail injection arrangement by means of the high-pressure pump. However, in order to supply the minimum pressure required for injection to the fuel rail, fuel supplied to the pump elements of the high-pressure pump may need to be initially pressurized.
Another reason for said initial pressure lies in the configuration of the high-pressure pumps used for common rail injection arrangements, these pumps being lubricated by means of the fuel. Accordingly, high-pressure may require a virtually uninterrupted supply of fuel to their bearings. This applies especially to operating states in which the pump shaft is rotating under load. For this purpose, a lift pump or pre-supply pump, is included to pump fuel from the fuel tank to the high-pressure pump.
Pre-supply pumps are conventionally electric. Electric pre-supply pumps can be switched on and off in a flexible manner when operating conditions allow, thus reducing the energy required to drive the pre-supply pump and hence increasing fuel efficiency and lowering noise levels.
The additional use of electric pre-supply pumps allows uninterrupted lubrication of the high-pressure pump with fuel and enables the internal combustion engine to be put into operation more quickly when exiting from a stop phase.
However, the inventors herein have recognized potential issues with such systems. As one example, the pre-supply pump may continue to run during a stop phase in a stop-start system, thereby increasing energy consumption and reducing fuel efficiency during the stop phase. Additionally, operation of the pre-supply pump may be perceptible and objectionable to a vehicle occupant via vibration and/or noise, especially when the internal combustion engine is switched off.
As one example, the issues described above may be addressed by a method for operating a common rail injection arrangement, which is provided for an internal combustion engine having a stop-start system and which comprises a pre-supply pump, connected to a high-pressure pump in a manner which allows fluid transfer, and a manifold, connected to the high-pressure pump in a manner which allows fluid transfer, as well as at least one injection nozzle, connected to the manifold in a manner which allows fluid transfer, wherein the pre-supply pump is kept active when the internal combustion engine is in operation, may comprise: initiating a stop phase by putting the running internal combustion engine and the high-pressure pump out of operation, wherein the pre-supply pump may be switched to the inactive state, initiating a starting phase for the out-of-operation internal combustion engine, wherein the high-pressure pump may be operated at least temporarily in an unpressurized state before or during the starting phase of the internal combustion engine, while the pre-supply pump is switched to the active state and delivers fuel to the high-pressure pump and builds up pre-supply pressure, operating the high-pressure pump to maintain and/or increase the pressure within the common rail injection arrangement, when a pre-supply pressure increases above a threshold, and starting the internal combustion engine by cranking the engine and injecting fuel into a combustion chamber of the internal combustion engine with the aid of the pressure provided within the common rail injection arrangement.
In another representation a system for a common rail injection arrangement of a stop-start engine may comprise: a high-pressure fuel pump, a pre-supply pump, connected to a high-pressure fuel pump in a manner which allows fluid transfer, wherein the pre-supply pump is kept active when the internal combustion engine is in operation, a manifold, connected to the high-pressure pump in a manner which allows fluid transfer, at least one injection nozzle, connected to the manifold in a manner which allows fluid transfer, and a controller with computer readable instructions stored in non-transitory memory for: initiating a stop phase by putting the running internal combustion engine and the high-pressure pump out of operation, wherein the pre-supply pump is also switched to the inactive state, maintaining, within the common rail injection arrangement, a pressure built up by the high-pressure pump during the operation of the internal combustion engine, wherein the pre-supply pump is simultaneously kept inactive, initiating a starting phase for the out-of-operation internal combustion engine, wherein the pre-supply pump is switched to an active state, starting of the internal combustion engine by cranking the latter and at least partial injection of fuel into a combustion chamber of the internal combustion engine with the aid of the pressure maintained within the common rail injection arrangement, wherein the high-pressure pump is operated at least temporarily in an unpressurized state during the starting, and switching the high-pressure pump into a pressurized state to maintain and/or increase the pressure within the common rail injection arrangement, in response to a pre-supply pressure increasing above a threshold to continue supplying the running internal combustion engine with fuel.
In yet a further representation, a method for a stop-start engine may comprise during an engine stop: powering off a lift pump, and in response to determining an engine start is desired: powering on the lift pump, initiating cylinder combustion, and operating a higher pressure pump (HPP) in an unpressurized mode, and switching the HPP to a pressurized mode in response to fuel pressure upstream of the HPP reaching a threshold. In the above method, a volume control valve may be positioned between the HPP and the lift pump, and may be adjusted to a closed position in the unpressurized mode, where in the closed position of the volume control valve, substantially no fuel flows flow there-through. In some examples, the operating the HPP in the unpressurized mode may comprise maintaining the volume control valve in the closed position during both intake and compression strokes of the HPP. Further, the switching the HPP to the pressurized mode may comprise opening the volume control valve to supply fuel to the higher pressure pump. In other examples, an inlet valve may be positioned between the lift pump and a single pressure chamber of the lift pump for regulating fuel flow there-between. In the unpressurized mode, the inlet valve may be adjusted to an open position to allow fuel between the lift pump and the higher pressure pump to increase a pressure of fuel supplied to the higher pressure pump.
In this way, fuel pressure in a fuel rail and fuel injectors may be maintained during an engine stop and fuel in a higher pressure pump may be expelled from the pump by closing a valve positioned between a lift pump and a higher pressure pump. As such, fuel injection delays during a subsequent engine start may be reduced, and fuel may more quickly be injected to facilitate an engine start after an engine stop. Further, by powering on the lift pump and operating the higher pressure pump in an unpressurized mode prior to and/or during the engine start, a pressure of fuel supplied to the higher pressure pump during the engine start may be increased. Operating the higher pressure pump in the unpressurized mode during the engine start may reduce strain on the higher pressure pump, and increase longevity of the pump. Additionally, by powering on the lift pump and operating the higher pressure pump in an unpressurized mode prior to and/or during the engine start, fuel pressure may be added to the fuel rail and fuel injectors more quickly during an engine start, further reducing any delays in fuel delivery to one or more engine cylinders. Thus, the fuel system may be more responsive and fuel delivery may be more immediate. Further, by powering off the lift pump during an engine stop, noise and energy consumption may be reduced.
In the description herein, a pre-supply pump may also be referred to as a lift pump, lower pressure pump (LPP), and low-pressure pump.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.